It has been known a rotary actuator in which an output rotation from a motor is reduced in speed via a strain wave gearing and is output therefrom. As disclosed in Patent document 1, the rotary actuator of this configuration has a strain wave gearing, a motor and an encoder (a brake mechanism) arranged in the axial line direction, and the dimension thereof in the axial line direction becomes large.
Patent Document 2 discloses a rotary actuator having a strain wave gearing and a motor assembled in a hollow part of the strain wave gearing. In this rotary actuator, the motor of outer rotor type has a rotor constituted by the rigid plug of a wave generator of the strain wave gearing and a rotor magnet adhered on the inner peripheral surface of the rigid plug. With this structure, a flat rotary actuator having a small dimension in the axis line direction is obtained.